Method for controlling acarids with phosphine oxides

ABSTRACT

Acarids, including spider mites, are effectively controlled by applying to the acarids, their habitat or both certain tertiary bis(halophenyl)phosphines, phosphine oxides and phosphine sulfides. These compounds kill adult and nymph acarids in addition to their eggs.

BACKGROUND

This invention relates to the control of acarids. This invention furtherrelates to compositions for controlling acarids, including mites, thatcan be applied directly to these organisms, their eggs or to areas,particularly plants, that are infested with these organisms.

Numerous phosphorus compounds have been disclosed as being effectivecontrol agents for acarids. For example, U.S. Pat. No. 2,754,242 teachesusing alkyl bis(halophenyl)phosphinates to kill two-spotted spidermites. Many of these compounds are not practical for use as commercialinsecticides, since they must be present at relatively highconcentration levels (500 parts per million or more) to be effective.The in-use cost of these prior art materials may therefore be so high asto exclude them for large-scale applications.

It has now been found that certain tertiary bis(halophenyl)phosphines,phosphine oxides and phosphine sulfides are remarkably effectiveacaricides that can be employed at lower concentration levels thanheretofore possible using many structurally related prior at materials,including those disclosed in the aforementined U.S. Pat. No. 2,754,242.

SUMMARY OF THE INVENTION

This invention provides a method for controlling acarids by applying tosaid acarids their eggs or to substrates susceptible to infestation withsaid acarids an acaricidally effective amount of a phosphorus compoundexhibiting the formula ##SPC1##

Wherein R is selected from the group consistng of alkyl radicalscontaining between 1 and 12 carbon atoms, alkenyl and alkynyl radicalscontaining between 2 and 12 carbon atoms, cycloalkyl, aryl, alkaryl,aralkyl and haloalkyl radicals, X represents a halogen atom selectedfrom the group consisting of fluorine, chlorine, bromine and iodineatoms and Z represents oxygen or sulfur.

DETAILED DESCRIPTION OF THE INVENTION

The present acaricides are tertiary bis(p-halophenyl) phosphines,phosphine oxides and phosphine sulfides. When R of the precedingformulae represents an alkyl radical, it may contain one or more halogenatoms as substituents. These compounds effectively control acarids,including spider mites, at considerably lower concentrations than can beachieved using structurally related compounds, such as theaforementioned bis(halophenyl)phosphinates that are disclosed in thechemical and patent literature. The comparative efficacy of the presentacaricides and the criticality of the substituents on both the phenylradicals and the phosphorus atom are demonstrated in the accompanyingexamples. In addition to killing nymph and adult acarids, the presentcompounds also inhibit development of the eggs of these organisms.

While many known acaricides are effective when sprayed onto plant leavesinfested with mites, the present compounds are unique in that they canalso be applied to the soil surrounding the roots of the plant and aretransported by the plant to the leaves, where both mites and their eggsare killed.

Many of the present tertiary bis(halophenyl)phosphines are disclosed inthe chemical literature. The phosphines are conveniently prepared byreacting the appropriate halophenyl magnesium halide anddichloroorganophosphine. The dichloroorganophosphines are eitheravailable from commercial suppliers or can be synthesized using knownpreparative methods, for example those disclosed in "Organ-phosphorusCompounds" by G. M. Kosolapoff, published by John Wiley and Sons, Inc.The resultant bishalophenyl)organophosphine is readily converted to thecorresponding phosphine oxide or phosphine sulfide by reacting thephosphine with hydrogen peroxide or elemental sulfur, respectively.

Alternatively, the phosphine oxides can be prepared directly from ahalophenylmagnesium halide by reacting it with the appropriateorganophosphonic dichloride, ##STR1##

The following examples provide specific methods for preparingrepresentative compounds encompassed by the accompanying claims. Allparts and percentages are by weight.

EXAMPLE 1 Bis(p-chlorophenyl)methylphosphine Oxide

To 900 cc. of a solution containing 1.143 moles ofp-chlorophenylmagnesium bromide dissolved in tetrahydrofuran was added73 g. (0.55 mole) of methylphosphonic dichloride ##STR2## dissolved in400 cc. of tetrahydrofuran. The addition required two hours, duringwhich time the reaction mixture was stirred and the temperaturemaintained at between 30° and 40° C. Following completion of theaddition the reaction mixture was heated to the boiling point for onehour, cooled and then extracted using 2 liters of chloroform. Thechloroform layer was then dried using anhydrous magnesium sulfate andthe solvent removed under reduced pressure. The solid residue wasrecrystallized once from benzene to yield 90 g. of a white solid thatmelted between 167° and 169° C. Analysis of the recrystallized productrevealed a phosphorus content of 10.9% and a chlorine content of 22.3%.The calculated phosphorus and chlorine content ofbis(p-chlorophenyl)methylphosphine oxide is 10.9 and 24.9%,respectively. The structure of the compound was confirmed by nuclearmagnetic resonance.

Example 2 Bis(p-chlorophenyl)chloromethylphosphine Oxide

To a solution containing 69 g. (0.39 mole) of chloromethylphosphonicdichloride and 400 cc. tetrahydrofuran was added 285 cc. of atetrahydrofuran solution containing 0.789 mole ofp-chlorophenylmagnesium bromide. The addition was dropwise and requiredtwo hours, during which time the temperature of the reaction mixture wasmaintained at 30° C. Following completion of the addition the mixturewas stirred for two hours while the temperature was maintained at 60° C.After the mixture had cooled to ambient temperature 400 cc. of waterwere gradually added, followed by 1200 cc. of methylene chloride. Theorganic layer was then separated, dried using anhydrous magnesiumsulfate and the methylene chloride removed under reduced pressure. Theresidue was passed through a column of neutral alumina using ethylacetate as the eluent. The white solid obtained following removal of theeluent and one recrystallization of the residue from benzene weighed 90g., melted between 114° and 117° C. and exhibited the followinganalysis: chlorine -- 32.8%; phosphorus -- 9.89%. The calculated valuesfor bis(p-chlorophenyl)chloromethylphosphine oxide are 33.3 and 9.70%,respectively. The nuclear magnetic resonance spectrum was consistentwith the desired structure.

EXAMPLE 3 Bis(p-chlorophenyl)methylphosphine

To 12.6 g. of magnesium turnings was gradually added a solutioncontaining 96 g. (0.50 mole) of p-chlorobromobenzene and 1.80 cc.tetrahydrofuran. The reaction mixture was stirred and maintained under anitrogen atmosphere during the addition, following which the contents ofthe vessel were heated to reflux temperature for two hours. When thereaction mixture had cooled, a solution of methyldichlorophosphine (29.3g., 0.25 mole) in 25 cc. tetrahydrofuran was gradually added. Followingcompletion of this addition the reaction mixture was heated to refluxtemperature for two hours. When the mixture had cooled it was slowlypoured into 500 cc. of cold water and then acidified to a pH of 5 usingaqueous hydrochloric acid. The resultant aqueous solution was extractedusing chloroform. The organic layer was then dried over anhydrousmagnesium sulfate and the chloroform removed under reduced pressure. Theresidue remaining followng removal of the chloroform weighed 64 g. andwas distilled, the fraction boiling at between 155 and 160 under apressure of 0.5 mm Hg being collected. This distillate converted to awhite solid upon cooling. The solid material weighed 34 g. and exhibitedthe following analysis:

    ______________________________________                                                     Found     Calculated                                             ______________________________________                                        Phosphorus     10.9%       11.5%                                              Chlorine       25.9%       26.4%                                              ______________________________________                                    

EXAMPLE 4 Bis(p-chlorophenyl)propylphosphine Sulfide

Bis(p-chlorophenyl)propylphosphine was prepared by reacting 0.2 mole ofpropyldichlorophosphine with a 0.4 mole of p-chlorophenylmagnesiumbromide. The product was isolated by chloroform extraction anddistillation as previously described. The portion boiling between 160°and 165° C. under a pressure of 2 mm. Hg was collected. The analysiscorresponded to bis(p-chlorophenyl)propylphosphine.

An 18 g. (0.061 mole) portion of the phosphine was combined with 150 cc.benzene, followed by 2.1 g. (0.065 mole) of sulfur. The resultantmixture was stirred for one hour and the solvent removed under reducedpressure. Following one recrystallization from diethyl ether the solidproduct weighed 16 g. and melted between 102° and 107° C. This productwas found to contain 9.21% phosphorus, 22.2% chlorine and 8.33% sulfur.The calculated values for bis(p-chlorophenyl) propylphosphine sulfideare 9.42, 21.6 and 9.73%, respectively.

When employed to combat acarids, particularly mites, the presentphosphines, phosphine oxides and phosphine sulfides can be applieddirectly on the acarids, to plants infested with acarids or to plantsand other substrates which are susceptible to attack by acarids. Thelong term residual activity and low phytotoxicity that characterize thepresent acaricides makes it possible to apply these compounds to plantsseveral days, and in some instances weeks, prior to the time when theplant will be exposed to the acarids.

The present compounds are conventionally applied to plants as liquidsprays, solid dusts or wettable powder.

Compositions suitable for spraying are usually prepared by dilutingliquid concentrates or wettable powders containing between 10 and 90% ofthe active toxicant. To avoid the expense of transporting formulationscontaining large amounts of inert diluents, the dilution is usuallyperformed at the location where the spray will be applied. Theconcentration of toxicant in a spray to be applied to plants in a fieldis between 10 and 1000 parts per million (ppm), preferably between 100and 500 parts per million.

Solid dust compositions, which are generally applied over a relativelysmall area, contain between 1 and 50% by weight of active toxicant,preferably between 1 and 10%.

The concentration of toxicant required in a given formulation will bedependent upon a number of parameters including the method ofapplication, i.e. whether at ground level or from aircraft, the activityof the particular toxicant against the acarid and weather conditions inthe area being treated.

In the preparation of dust compositions or wettable powders, the presentacaricides can be blended with many commonly employed finely dividedsolids, such a as s earth, attapulgite, bentonite, pyrophyllite,vemriculite, diatomaceous earth, talc, chalk, gypsum, wood flour, andthe like. The finely divided carrier is ground or mixed with theacaricidal toxicant or wetted with a dispersion of the toxicant in avolatile liquid. Depending upon the proportions of ingredients, thesecompositions can be employed as concentrates and subsequently dilutedwith additional solid carriers to obtain the desired amount of activetoxicant. Also, such concentrate dust compositions can be incorporatedin intimate admixture with surface active dispersing agents such asionic or nonionic emulsifying or dispersing agents to form sprayconcentrates. Such concentrates are readily dispersible in liquidcarriers to form spray compositions or liquid formulations containingthe toxicants in any desired amount. The choice of surface active agentand amount employed are determined by the ability of the agent tofacilitate the dispersing of the concentrate in the liquid carrier toproduce the desired liquid composition. Suitable liquid carriers includewater, methanol, ethanol, isopropanol, methyl ethyl ketone, acetone,methylene chloride, chlorobenzene, toluene, xylene, and petroleumdistillates. Among the preferred petroleum distillates are those boilingalmost entirely under 205° C. at atmospheric pressure and having a flashpoint above about 30° C.

Alternatively, the acaricide may be compounded with a suitablewater-immiscible organic liquid and a surface active dispersing agent toproduce emulsifiable concentrates which may be further diluted withwater and oil to form spray mixtures in the form of oil-in-wateremulsions. In such compositions, the carrier comprises an aqueousemulsion, i.e. a mixture of water-immiscible solvent, emulsifying agentand water. Preferred dispersing agents which may be employed in thesecompositions are oil soluble and include the condensation products ofalkylene oxides with phenols and organic or inorganic acids,polyoxyethylene derivatives of sorbitan esters, alkylarylsulfonates,complex ether alcohols, mahogany soaps and the like. Suitable organicliquids to be employed in the compositions include petroleumdistillates, hexanol, liquid halohydrocarbons and synthetic organicoils. The surface active dispersing agents are usually employed in theliquid dispersions and aqueous emulsions in the amount of from about 1to about 20 percent by weight of the combined weight of the dispersingagent and the active toxicant.

The following examples demonstrate the efficacy of the present compoundsas acaricides. Formulations were prepared by dissolving the compound tobe tested in a mixture of acetone and a liquid alkyl-aryl polyetheralcohol type surfactant (Triton X-155) and diluting the resultantcomposition to the desired concentration using a water-acetone mixturesuch that the final formulation contained 10% acetone and 10 parts permillion (ppm) of the surfactant.

The activity of a given compound as a contact acaricide against thetwo-spotted spider mite (Tetranychus urticae) was determined bytransferring adult and nymph mites to the leaves of Sieva lima beanplants. Twenty four hours following the transfer the leaves were eithersprayed with or dipped into the aforementioned formulation containing200 ppm of the compound to be tested. If the compound was to beevaluated as a systemic acaricide and ovicide 21 cc. of a formulationcontaining 520 ppm of the active compound was poured into the soilsurrounding the infested plant.

Nine to twelve days following application of the formulation the leavesof all plants were examined using a microscope to determine the numberof dead mites and eggs.

The following compounds were found to be effective contact typeacaricides at a concentration of 200 ppm, in that they killed at least70% of the adult mites, nymphs and/or eggs.

bis(p-chlorophenyl)ethylphosphine oxide

bis(p-chlorophenyl)ethylphosphine

bis(p-chloropenyl)methylphosphine oxide

bis-(p-chlorophenyl)chloromethylphosphine oxide

bis(p-chlorophenyl)propylphosphine oxide

bis(p-chlorophenyl)methylphosphine sulfide

bis(p-chlorophenyl)methylphosphine

bis(p-chlorophenyl)propylphosphine

bis(p-bromophenyl)methylphosphine oxide

bis(p-fluorophenyl)methylphosphine oxide

The following compounds, which are structurally related to the presentacaricides, were ineffective in controlling spider mites or their eggs(less than 30% of mites or eggs killed) at a concentration of 200 ppm.

diphenylmethylphosphine oxide

diphenylchloromethylphosphine oxide

bis(p-chlorophenyl)trichloromethylphosphine oxide

bis(m-chlorophenyl)methylphosphine oxide

tris(p-chlorophenyl)phosphine oxide

bis(p-chloro-m-nitrophenyl)methylphosphine oxide

bis(p-tolyl)methylphosphine oxide

bis(m,p-dichlorophenyl)methylphosphine oxide

bis(p-chlorophenyl)hydroxymethylphosphine oxide

bis(p-chloro-o-methylphenyl)methylphosphine oxide

Two of the most effective acaricides, bis(p-chlorophenyl)methylphosphineoxide (A) and bis(p-chlorophenyl) chloromethylphosphine oxide (B) wereevaluated further to ascertain the lowest concentration at which thesecompounds are effective. The data from this test are summarized in thefollowing table, together with the results obtained usingN'(4-chloro-o-tolyl)N,N-dimethylformamidine (Galecron), a commerciallyaccepted miticide and ovicide. All plants were rated twelve days afterbeing sprayed with the test formulation.

    __________________________________________________________________________              CONCENTRATION                                                                           % CONTROL OF                                                                           No. OF                                           COMPOUND  (PPM)     ADULT MITES                                                                            DEAD EGGS                                        __________________________________________________________________________    A         400       100      525                                                        100       68       545                                                         25       53       --                                               B         400       100      605                                                        100       90       670                                                         25       94       --                                               Galecron (control)                                                                      400       65       135                                                        100        0       --                                                          25        0       --                                               __________________________________________________________________________

A formulation containing 100 ppm ofbis(p-chlorophenyl)chloromethylphosphine oxide was poured onto the soilsurrounding the roots of a Sieva lima bean plant which was infested withspider mites and eggs. Six days later 97% of the adult mites and 90% ofthe eggs were dead on one leaf. Examination of a second leaf revealedthat 100% of the eggs had been killed.

What is claimed is:
 1. A method for controlling acarids by applying tothe acarids, their eggs or to substrates susceptible to infestation withsaid acarids an acaricidally effective amount of a phosphorus compoundexhibiting the formula ##SPC2## wherein R is selected from the groupconsisting of alkyl containing 1 to 12 carbon atoms, haloalkylcontaining 1 to 12 carbon atoms, alkenyl containing between 2 and 12carbon atoms and alkynyl containing between 2 and 12 carbon atoms, Xrepresents a halogen atom selected from the group consisting offluorine, chlorine, bromine and iodine and Z represents oxygen orsulfur.
 2. The method of claim 1 wherein the phosphorus compound ispresent in combination with an inert liquid or inert solid diluent at aconcentration of between 1 and about 500 parts per million.
 3. Themethod of claim 1 wherein R represents an alkyl containing from 1 to 12carbon atoms.
 4. The method of claim 1 wherein R is methyl, ethyl,propyl or chloromethyl.
 5. The method of claim 1 wherein X is chlorine.6. The method of claim 1 wherein the substrate is a plant.
 7. The methodof claim 6 wherein the phosphorus compound is applied to the leaves ofsaid plant.
 8. The method of claim 6 wherein the phosphorus compound isapplied to the soil adjacent to the roots of said plant.